1. Field of the Invention
The present invention generally relates to apparatus for restoring lost data to an electrically powered memory device in a photographic camera. More particularly, the invention relates to apparatus for restoring film-related data that is lost from storage in the memory device because of a power diminution or a power interruption resulting, for example, from a weak or dead battery in the camera.
2. Description of the Prior Art
It is known to provide an electrically powered memory device in modern cameras, especially 35 mm cameras. The memory device may be used as a counter which monitors the movement of a filmstrip in the camera. For example, in U.S. Pat. No. 4,021,828, granted Feb. 3, 1975, after the camera is loaded with fresh film, the counter is set to a value corresponding to the total number of frames on the filmstrip, e.g. 12, 24 or 36 frames. A sprocket wheel engaging successive sprocket holes in the filmstrip makes one rotation each time the filmstrip is advanced a single frame length. A differentiating circuit, coupled with the sprocket wheel, applies an output pulse to the counter each time the sprocket wheel makes one rotation. The output pulses are counted up or down with respect to the value set in the counter to enable an indicator to display the number of exposed or unexposed frames.
German Offenlegungsschrift No. 28 33 550, published Feb. 15, 1979, discloses a pair of electrodes arranged on opposite sides of the path of successive sprocket holes in a filmstrip advanced in the camera. A pulse generating circuit, coupled with the electrodes, applies an output pulse to a counter each time the electrodes detect a sprocket hole. The count of output pulses is used to control film metering and, following advance of the filmstrip a frame length, to display the number of frames still available for exposure.
In the '828 patent and the '550 Offenlegungsschrift, the various battery powered elements, other than the counter which stores the pulse count, may be disconnected from the battery during the time interval between successive film winding operations to prevent wasteful consumption of the battery. The counter is not disconnected from electrical power because it has a volatile memory.
Known cameras that include a counter having a volatile memory typically suffer certain disadvantages. For example, in the '828 patent and the '550 Offenlegungsschrift, should the battery source of electrical power become weak or die, causing the pulse count to be lost, the lost count is not restored upon replacing the used battery with a fresh one. If the battery failure occurs before all of the available film frames have been exposed, then, after replacing the used battery with a fresh one and exposing the next available film frame, the pulse count will be incorrect. An improper pulse count will, of course, result in the indicator displaying an incorrect number and may affect other camera operations, such as film metering, which depend upon the pulse count.